<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    /*（1）利用浮动，将左边元素宽度设置为200px，并且设置向左浮动。将右边元素的margin-left设置为200px，宽度设置为auto（默认为auto，撑满整个父元素）。*/
    .router {
      height: 100px;
    }

    .left {
      float: left;
      width: 200px;
      height: 100px;
      background-color: tomato;
    }

    .right {
      margin-left: 200px;
      /* width: auto; */
      height: 100px;
      background-color: gold;
    }
  </style>
</head>

<body>
  <div class="router">
    <div class="left">left200px</div>
    <div class="right">right自适应</div>
  </div>
</body>

</html>